Common unfoldable chairs have the advantage that they have a strong structure to withstand a heavy load. However, they have the disadvantage that they cannot be folded so that they must occupy a fixed space, which is inconvenient for storage or transportation. Alternatively, although there have been many types of folding chair which have been sold in the market, these conventional folding chairs have a relatively weak structure so that after a period of use they may lose their original rigidity and firmness.